Integrated multilayer fabrics have wide applications such as advanced composites, power transmission and conveyer belts, fabrics in paper forming machines, among others.
Advanced composites include high performance fibers in a matrix. Depending on the fibers and matrix materials and manufacturing parameters, advanced composites offer superior strength-to-weigh and modulus-to-weight ratios, fatigue strength, damage tolerance, tailored coefficient of thermal expansion, chemical resistance, weatherability, temperature resistance, among others.
Fibers are the basic load-bearing component in a fiber reinforced composite. They are often pre-assembled into various forms to facilitate the fabrication of composite parts. Advanced composites are often made from prepreg tapes, sheets and fabrics that are parallel continuous fibers or single-layer fabrics held by a matrix forming material. They are used to make parts by laminate layup and tape or filament winding. The traditional laminated composites are vulnerable to delamination because the layers of strong fibers are connected only by the matrix material that often is much weaker than the fibers. The introduction of fiber reinforcement in the through-the-thickness direction in a three dimensional composite could effectively control delamination failures and make the composite very damage tolerant. Besides performance enhancement, composites reinforced with integrated fiber structures may also offer other advantages such as the potential for automated and net shape processing and lower manufacturing cost.
Planar multilayer fabrics having layers of parallel fibers at predetermined angles bound by a knitting process, known as non-crimp fabrics, are also commonly used in reinforced composites. Methods of making such multilayer fabrics are disclosed in U.S. Pat. No. 4,518,640 to Wilkens. These methods are suitable for making flat fabrics with fixed width and yarn orientations. The in-plane layers normally include high performance fibers such as glass and/or graphite fibers, whereas the knitting yarns generally are made of flexible fibers such as poly(ethylene terephthalate) (PET) or aramid rather than using the same type of high performance fibers as in the in-plane layers.
Fabrics with solid rectangular or other cross sectional shapes such as I and T sections may be constructed with reinforcing fibers in both in-plane and through-the-thickness directions by three dimensional weaving and braiding processes, as disclosed in, for examples, U.S. Pat. No. 4,312,261 to Florentine and U.S. Pat. No. 5,085,252 to Mohamed et al. These processes are generally limited in the cross sectional shapes and dimensions of the fabrics that can be produced.
Fully interlocked and adjacent layer interlocked three dimensional fabrics may be formed by weaving or braiding. Hollow fabrics such as tubular structures may be made according to, for example, U.S. Pat. No. 4,174,739 to Rasero et al. In such fabrics the yarns are crimped due to yarn interlacing or intertwining, and the yarn crimps in the fabrics cause a reduction in the stiffness and strength of the composites reinforced with such fabrics. Although the fabrics layers are integrated by interlocking, there are no reinforcing yarns placed directly in the through-the-thickness direction.
Composite parts reinforced with hollow fabrics are widely used for many applications. The composites are often constructed from flat fabrics in which the fibers are discontinuous. Hollow fabrics such as tubular fabrics may be constructed directly from yarns, and the yarns are primarily placed in the axial, radial and circumferential directions, as disclosed in, for example, U.S. Pat. No. 4,001,478 to King, and U.S. Pat. No. 4,346,741 to Banos et al. and U.S. Pat. No. 6,129,122 to Bilisik. Such fabrics do not afford the flexibility of changing the fabrics geometry and yarn orientation at different locations in the fabrics as needed. The traditional integrated hollow fabrics lack the flexibility of varying the fiber orientation and/or the cross sectional shape and/or dimension as the fabrics are being formed. They are often associated with other disadvantages such as low fiber volume fraction, limitation in fiber orientations, and forming a net-shaped structure, among others.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.